The present invention relates to improved catalysts for use in the hydroxylation of benzene or derivatives thereof to form phenol or related compounds.
Phenol or a derivative thereof can be produced by a single-step oxidative hydroxylation of benzene or a derivative thereof, using nitrous oxide over a catalyst. For example, PCT publication WO 95/27560 describes such a process that employs a zeolite catalyst whose performance is enhanced by hydrothermal treatment. The zeolite catalyst is treated with a water vapor-containing gas phase at a temperature in the range of 350.degree. to 950.degree. C. Zeolite catalysts that have been hydrothermally treated in this fashion are characterized by relatively stable performance. In other words, when such a hydrothermally treated catalyst is used in a process to convert benzene to phenol by oxidation with nitrous oxide, the reduction in benzene conversion as time passes is less than it would be if the catalyst had not been hydrothermally treated.
However, a need remains for catalysts having further improved performance, so that a process for conversion of an aromatic hydrocarbon such as benzene to phenol or another desired product can be made more economical. Any improvements which increase catalyst stability and therefore increase the time between catalyst regeneration would enhance the commercial desirability of the process. Many of the efforts to date to achieve such additional catalyst improvements have focused on optimizing the hydrothermal treatment of the catalyst.